Set-top boxes (STB) that receive signals from satellite providers are well known in the art. These STBs are required to process two different types of signals. A first type of signal includes a frequency band that includes only satellite television data (e.g. legacy signal). A second type of signal has a portion of the satellite signal band reserved for networking data and the satellite signal is converted to single wire-multiswitch (SWM) signal. Typically, the band reserved for networking data is structured according to the Multimedia over Coax Alliance (MoCA) standards. Data in the MoCA band typically includes internet data that is transmitted from and received by the STB as well as local area networking data that allows multiple STBs in a particular location to communicate with one another. Thus, STB designers must provide a STB architecture that can receive and process both types of signals. An exemplary STB that can process both Legacy signals and SWM signals is shown in FIG. 1.
FIG. 1 is a block diagram of a conventional STB 1. The STB 1 includes a controller 30 that controls the complete operation of the STB 1. The STB 1 includes an F-connector 4 for receiving an RF input signal 2 from satellite receiver outdoor unit (a LNB or SWM unit, not shown). The manner in which the satellite signal is received and processed to generate the input signal 2 is well known and is not germane to the present invention. The STB 1 also includes a SWM circuit 7 which is a 2.3 MHz FSK transceiver. The SWM circuit 7 sends commands to an outdoor SWM unit in order to move the satellite transponder to a SWM channel. Additionally, the SWM circuit 7 may also receive the status/response of outdoor unit and provide that information to the controller 30. The input signal 2 received via the F-connector 4 is a full spectrum signal and ranges from 22 kHz-2150 MHz for a legacy signal or 2.3 MHz-2150 MHz for a SWM signal. The full spectrum input signal 2 is provided to a first diplexer 6. The first diplexer 6 includes a first high pass filter (HPF) 8 that attenuates the signal to enable a portion of the signal greater than 950 MHz to pass therethrough. The first diplexer 6 also includes a first low pass filter 9 that attenuates the signal such that the portion of the signal below 816 MHz is allowed to pass therethrough. The portion of the signal 2 filtered by the first low pass filter 9 is generally includes digital television data formatted in accordance with the Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) standard. The part of the signal filtered by low pass filter 9 also includes the FM broadcast band, 88-108 MHz which is an undesired signal. A high pass filter 13 having a cutoff frequency of substantially 174 MHz is connected to an output of the first low pass filter 9 and receives the portion of the signal 2 filtered by low pass filter 9. The high pass filter 13 removes FM band, SWM tone or DisEqC tone. In legacy mode, a 22 kHz DisEqC signal is used to send commands to outdoor unit, such as LNB, or outdoor antenna switch. In SWM mode, the 2.3 MHz FSK signal is used to communicate with the outdoor SWM module, to assign a SWM channel to a satellite transponder coming from the satellite antenna and this signal is processed by SWM circuit 7 discussed above. The ISDB-T data is provided to an ISDB-T tuner 10 for tuning thereof. The tuned signal is provided to the ISDB-T demodulator 11 for demodulation. The demodulated signal is provided to the controller 30 which may perform further processing as is known in the art and route the demodulated ISDB-T signal to a respective output 34. A single output 34 is shown here for purposes of example only and, as is well known in the art of STB design, the STB 1 may include a plurality of different output connectors for connecting the STB 1 to a display screen or monitor. Outputs may include but are not limited to an HDMI port, a composite video port, component video ports, DVI ports, VGA ports and a Coaxial output port.
The portion of the signal having a frequency greater than 950 MHz is filtered by the first high pass filter 8 and is further provided to the first switch 12. The first switch 12 may be a single pole double through switch that is selectively controllable to define the path taken by the portion of the signal filtered by HPF 8. The controller 30 is pre-programmed upon setup thereof to receive and process either a legacy signal or a SWM signal. If the controller 30 determines that the signal to be processed by the STB 1 is a legacy signal, the first switch 12 is configured to pass the signal filtered by the first HPF 8 to the second switch 22. The second switch 22 provides the filtered satellite signal to a legacy tuner (also called network tuner) 24 for tuning thereof. The filtered satellite signal is spilt by the legacy tuner 24 and one output is provided to a legacy Demod 25 of the controller while the other output is amplified by amplifier 26 and passed through a balun 28 before being received by the A3 tuner and Demod 29 of the controller 30. At least one of the legacy Demod 25 and the A3 tuner and Demod 29 provide the signal to a respective output 34 for display on a display device as is known in the art.
Upon determining by the controller 30 that the signal received at the F-connector 4 is a SWM signal, the first switch 12 is configured to allow the portion of the signal filtered by the first HPF 8 to be provided to a second diplexer 14. The second diplexer 14 includes a second HPF 18 for filtering portions of the signal below substantially 1250 MHz and a second LPF 16 for filtering portions of the signal above substantially 1050 MHz. The output of the second LPF 16 is a signal having a frequency band ranging between substantially 950 MHz and 1050 MHz. The data in this frequency band represents MoCA data and is provided to the MoCA module 21 of the controller 30 via the MoCA transceiver 20. The manner in which the MoCA data is processed is well known and need not be further discussed.
The output of the second HPF 18 of the second diplexer 14 is a signal having a frequency band ranging between substantially 1250 MHz and 2150 MHz which represents the satellite data. The signal output by the second HPF 18 is provided to the second switch 22 and is output to the legacy tuner 24. This signal is processed in a manner similar to that described above and need not be repeated.
Thus, in order to have a STB able to process both legacy and SWM signals, conventional STB 1 includes a dual diplexer architecture such as shown in greater detail in FIG. 2. FIG. 2 is a more detailed view of the dual diplexer architecture described above in FIG. 1. In FIG. 2, the first diplexer 6 is connected at the F-connector 4 to provide a first filtered signal having a frequency substantially below 806 MHZ and a second filtered signal having a frequency band ranging substantially between 950 MHz and 2150 MHz. The first filtered signal includes ISDB-T formatted digital television data while the second filtered signal includes satellite data if the input signal 2 is a legacy signal or includes MoCA and Satellite data if the input signal 2 is a SWM signal. If the signal filtered by the first diplexer 6 is a legacy signal, the entire spectrum of the signal greater than 950 MHz is provided to the tuner as discussed above. In contrast, if the signal filtered by the first diplexer 6 is a SWM signal, the filtered signal is provided to the second diplexer 14 for further filtering to produce an output signal that includes only the frequency band containing MoCA data and a further output signal that includes the frequency band that includes the satellite television data for tuning.
A drawback associated with the convention STB design exhibited in FIGS. 1 and 2 is that the second diplexer 14 which is supposed to generate the MoCA signal and the satellite signal is difficult to design. This is because there is a small transient band. To be optimally effective, the second diplexer 14 needs substantially 50 dB MoCA rejection within the 100-200 MHz frequency band at substantially 1050 MHz. In view of the constraints associated with the rejection requirements as well as those inherent to the switch, it is difficult to obtain an acceptable level of return loss. Return loss is the loss of signal power resulting from the reflection of power on the transmission line. If the STB is unable to route the power applied thereto, it may be reflected back on the F-connector and output to other STBs connected on home network. This may negatively impact the performance of all STBs on the home network. Thus, the conventional STB design including two diplexers results in a sub-optimal level of return loss. Therefore, a need exists to provide a STB that can operate in both legacy and SWM modes while improving the amount of return loss in the system. A system according to invention principles remedies the drawbacks associated with these and other prior art systems.